Indicator for an optical instrument

ABSTRACT

An indicator for an optical instrument including an observational optical system to observe an image formed by an objective optical system having a focusing lens group, comprising a lens position detecting device to detect a position of the focusing lens group, a distance detecting device to obtain an object distance according to a position of the focusing lens group detected by the lens position detecting device, and a display device to display an object distance detected by the distance detecting device.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an indicator for an opticalinstrument, for example, an indicator applied to a surveying instrumentsuch as an auto-level or a transit instrument having a telephotographicsystem.

[0003] 2. Description of the Related Art

[0004] A surveying instrument such as an auto-level or a transitinstrument is basically provided with a collimating telescope, a level,and scales for measuring a rotative angle (an azimuth angle) or anelevational angle. A typical auto-level collimating telescope isprovided, in order from an object side, with an objective lens group, afocusing lens group, a horizontal compensation and erecting opticalsystem, and an eyepiece lens group. The position of the focusing lens isadjusted according to the distance from the object, so that an image ofthe object may be formed on a reticle (focusing plate). The operator maythus observe the image superimposed on the reticle via the eyepiece.

[0005] Surveying instruments, such as an auto-level, did not have adistance measuring apparatus that could indicate the distance to anobject, for example to a staff. In particular, although the auto-levelmay preferably be located at the equal distance position from twomeasuring points, the auto-level has no function to measure thedistance. Therefore in the prior art, the position of the auto-level hasusually been decided according to experience and intuition of theoperator. Accordingly, it would be convenient if the distance to themeasuring point could be made known to the operator.

[0006] A collimating telescope of surveying instrument in which anautomatic focusing apparatus is provided is well known. According to aconventional automatic focusing apparatus, even if accurate focusing isnot carried out, as long as the defocus is little enough so that theoperator may feel as though the image is focused, the focusing operationwould be stopped. However, the measuring of the object distance with theexistence of such a defocus may result in a large object distance error.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide an indicatorof an optical instrument to carry out focusing by moving a focusing lensgroup, in which an object distance observed by an operator can beindicated to the operator.

[0008] It is another object of the present invention to provide anautomatic focusing apparatus which can detect the object distance moreaccurately.

[0009] Since the distance of an object being viewed through a surveyinstrument having a collimating telescope is conventionally determinedas being the distance from the objective lens group of the collimatingtelescope to the focusing plate, if the focal length of the objectivelens group and the focusing lens group, and the distance between theobjective lens group and the focusing lens group are known, the objectd-stance can be readily determined. Namely, if the amount of movement ofthe focusing lens group from a reference position (for example, theposition of a focusing lens group in infinity) is detected, the distanceto the object can be obtained. Therefore, to achieve the objectmentioned above, according to the present invention, there is providedan indicator for an optical instrument including an observationaloptical system to observe an image formed by an objective optical systemhaving a focusing lens group, composing of: a lens position detectingdevice to detect a position of the focusing lens group, a distancedetecting device to obtain an object distance according to a position ofthe focusing lens group detected by the lens position detecting device,and an inside-visual-field display device to display an object distancein a visual field of the observational optical system detected by thedistance detecting device.

[0010] Further, according to an invention as claimed in claim 13, thereis provided an indicator for an optical instrument including anobservational optical system to observe an image formed on apredetermined focal plane by an objective optical system having afocusing lens group, composing of: a split optical system positionedbetween the objective optical system and the observational opticalsystem, a focusing detecting device to detect a defocus amount at aposition equivalent to the focal plane by receiving light divided by thesplit optical system, a lens driving device to drive the focusing lensgroup according to a defocus amount detected by the focusing detectingdevice so that the defocus amount becomes a smallest value, a lensposition detecting device to detect a position of the focusing lensgroup; an object distance detecting device to detect an object distanceaccording to a position of the focusing lens group detected by the lensposition detecting device and according to the defocus amount; and aninside-visual-field display device to display an object distance in avisual field of the observational optical system detected by the objectdistance detecting device.

[0011] The present disclosure relates to subject matter contained inJapanese Patent Application No. 09-133844 (filed on May 23, 1997) whichis expressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will be described below in detail with reference tothe accompanying drawings, in which:

[0013]FIG. 1 is a block diagram of main elements of an embodiment of anauto-level to which the present invention is applied;

[0014]FIG. 2 is a view of an embodiment of the visual field according tothe present invention;

[0015]FIG. 3 is a block diagram of main elements of another aspect of anauto-level to which the present invention is applied;

[0016]FIG. 4 is a view showing a mechanism of obtaining an objectdistance according to the embodiment of the present invention;

[0017]FIG. 5 is a flow chart showing a partial operation (START) in anautomatic focusing operation of an auto-level according to the presentinvention;

[0018]FIG. 6 is a flow chart showing a partial operation (VDD LOOP) inthe automatic focusing operation of the auto-level according to thepresent invention;

[0019]FIG. 7 is a flow chart showing a partial operation (AF OPERATION)in the automatic focusing operation of the auto-level according to thepresent invention;

[0020]FIG. 8 is a flow chart showing a partial operation (PULSECALCULATION) in the automatic focusing operation of the auto-levelaccording to the present invention;

[0021]FIG. 9 is a flow chart showing a partial operation (DRIVEDIRECTION CHECK) in the automatic focusing operation of the auto-levelaccording to the present invention;

[0022]FIG. 10 is a flow chart showing a distance indication operation ofthe auto-level according to the present invention; and

[0023]FIG. 11 is a flow chart showing the other distance indicationoperation of the auto-level according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will now be described in detail withreference to drawings attached hereto. FIG. 1 shows an embodiment of anauto-level to which an automatic focusing apparatus according to thepresent invention is applied. An auto-level 10 consists of a collimatingobjective lens group 11 of positive power and a focusing lens group 12of negative power which serve as the objective optical system, anoptical horizontal compensation system 13, a spilt optical system(divided optical system) 16, a first focusing plate 14 a and a secondfocusing plate 14 b to integrally serve as a focusing plate (reticle)14, and an eyepiece lens group 15 of positive power (observationaloptical system), in this order from the object side (left side of FIG.1).

[0025] The optical horizontal compensation system 13, per se known,consists of a first compensation prism 13 a, a compensation mirror 13 b,and a second compensation prism 13 c, and has a symmetrical shape. Theoptical horizontal compensation system 13 is hung from a shaft by astring or the like (not shown). The angle defined between thecompensation mirror 13 b and the first compensation prism 13 a isidentical (in absolute-value) to the angle defined between thecompensation mirror 13 b and the second compensation prism 13 c, but areopposite in direction. The angle, for example 30° varies depending onthe length of the string, etc. When the optical horizontal compensationsystem 13 is set so that the optical axes of the objective lens group 11and the focusing lens group 12 are substantially parallel (inclined at,for example, about 10 to 15 minutes with respect to the horizontalaxis), light incident upon the first compensation prism 13 a is deviatedfrom the horizontal direction by the same amount, but the lightreflected by and emitted from the first compensation prism 13 a, thecompensation mirror 13 b and the second compensation mirror 13 c, issubstantially collimated.

[0026] The focusing lens group 12 is provided with a rack 12 a securedthereto, which is engaged by a pinion 12 b. When a rotation of thepinion 12 b takes place to move the focusing lens group 12 in theoptical axis direction, the image of an object 9 formed by the objectivelens group 11 and the focusing lens group 12 is translated along theoptical axis. The operator views the object image formed on the focusingplate 14 together with the reticle etc., drawn on the focusing plate 14,through the eyepiece 15.

[0027] There is an indicator 17 provided under the focusing plate 14.The embodiment shown in FIG. 2 is the indicator 17 which indicates notonly the distance information to the object 9, but also whether or notthe focusing is completed, and whether the current focusing state is inauto-mode (AF) or manual-mode (MF).

[0028] A beam splitter (half mirror) 16 is provided in the light pathbetween the objective lens group 11 and the focusing plate 14 to splitthe light (or light path). A focus detecting system (focus detector) 20is provided in the split light path to detect the focus state (state ofthe formed image) at an equivalent surface 14A which is opticallyequivalent to the focusing plate 14. The focusing lens 12 is driven by alens driver (focusing lens group driving system) 30 in accordance withshe output of the focus detector 20.

[0029] The focus detector 20 includes an AF sensor 21 located in thevicinity of the equivalent surface 14A, so that the defocus amount(defocus, front focus, rear focus) can be detected in accordance withthe output of the AF sensor 21, of which structure is known per se. TheAF sensor in the present embodiment is a phase matching type, in whichthe object image on the equivalent surface 14A is split by a condenserlens and a pair of separator lenses (image forming lenses) spaced at adistance identical to the base length, and is re-formed on a pair of CCDline sensors. The CCD line sensors are each provided with a number ofphotoelectric transducers which convert the object image received intoelectrical charges which are integrated (accumulated). The integratedcharges are successively output as AF sensor data. The AF sensor data isamplified by a preamplifier 22 before being supplied to thecalculation/control circuit 23. The calculation/control circuit 23calculates the defocus amount through a predetermined defocuscalculation in accordance with the AF sensor data. In the illustratedembodiment, in addition to the defocus amount, the displacement anddirection of the movement of an AF motor 31 (the number of outputpulses, referred to hereinafter as “AF pulses” of an encoder 33)necessary to move the focusing lens 12 until the defocus amount becomeszero is also calculated in accordance with the defocus amount. Thenumber of AF purses is set in an AF pulse counter 23 a incorporated inthe calculation/control circuit 23.

[0030] The calculation/control circuit 23 drives the AF motor 31 throughan AF motor drive circuit 25, in accordance with the rotationaldirection of the AF motor 31, in order to be decrement the AF pulsecounter 23 a by detecting the output from the encoder 33. The rotationof the AF motor 31 is transmitted to the pinion 12 b through aclutch-incorporated reduction mechanism 32 to move the rack 12 a(namely, the focusing lens group 12). The calculation/control circuit 23also controls the driving speed and stopping of the AF motor 31 based onthe amount counted by the AF pulse counter 23 a. Namely, when thecounted amount is larger than a predetermined amount, the driving speedbecomes high, and when the counted amount is smaller than thepredetermined amount, the driving speed becomes low to allow braking,etc.

[0031] The calculation/control circuit 23 detects the defocus amount(i.e. detects focusing) against the object 9 by device of the focusdetector 20 and the lens driver 30, in order to move the focusing lensgroup 12 in the optical axis direction. Accordingly, when the absoluteamount of defocus is smaller than the predetermined amount, the lensdriver 30 stops at that point, being determined as in-focus. Thus thefocusing is essentially completed with respect to the object 9.

[0032] The focusing lens group 12 (rack 12 a) is provided with amovement detector 19 to detect the moving amount of the focusing lensgroup 12 from an infinity focal position. The distance to the object 9in a focused state is uniformly defined according to the focal lengthsof the objective lens group 11 and the focusing lens group 12, thedistance between the objective lens group 11 and the focusing plate 14,and the distance between the objective lens group 11 and the focusinglens group 12. Accordingly, when the moving amount of the focusing lensgroup 12 is detected by the movement detector 19, the distance to theobject 9 may be obtained. Thus the calculation/control circuit 23obtains the object distance based on the amount of movement of thefocusing lens group 12 detected by the movement detector 19, andindicates the obtained object distance on the indicator 17.

[0033] The movement detector 19 may include, for example, acode-plate/brush mechanism known per se, to detect the absolute positionof the focusing lens group 12. The movement detector 19 may alsoinclude, for example, an optical encoder which detects the relativeposition of the focusing lens group 12, namely the moving amount fromthe reference position (infinity focal position).

[0034] The focus detector 20 is provided with an AF start switch 27 tostart the automatic focusing operation, a focusing operation knob 34 tochange modes of focusing, and an AF switch 29 which detects the AF mode(that is, the mode which is not the manual focus mode).

[0035] The pinion 12 b is driven in either a manual focus mode by thefocusing operation knob 34, or in an autofocus mode, in which theautomatic focusing operation is carried out in accordance with the focusdetector 20 and the lens driver 30. Namely, the auto-level 10 isconstructed such that the focusing mode is switched between theautofocus mode, in which the focusing lens group 12 is driven inaccordance with the output of the focus detector 20, and the manualfocus mode, in which the focusing lens group 12 is driven manuallyregardless of the output of the focus detector 20.

[0036] For instance, when the focusing operation knob 34, whichconstitutes a mode switching device between the manual focus mode andthe autofocus mode, is moved in one axial direction, the manual mode isobtained, and when the focusing operation knob 34 is moved in anotheraxial direction, an autofocus mode (AF mode) is obtained. For example,when the focusing operation knob 34 is switched to the manual focusmode, the clutch-incorporated reduction mechanism 32 disconnects the AFmotor 31 from the reduction mechanism 32, and when the focusingoperation knob 34 is switched to the autofocus mode, theclutch-incorporated reduction mechanism 32 clutches the AF motor 31 withthe reduction mechanism 32. The clutch-incorporated reduction mechanism32 may either be constructed so as to maintain connection with thefocusing operation knob 34 at all times regardless of position (mode) ofthe focusing operation knob 34, or be constructed so as to disconnectfrom the focusing operation knob 34 when switched to the autofocus mode.The calculation/control circuit 23 detects whether the focusingoperation knob 34 is switched to the autofocus mode when the AF switch29 is turned OFF.

[0037]FIG. 3 shows another aspect according to the embodiment of thepresent invention, wherein the auto-level 10 according to the embodimentof FIG. 1 has an indication projector 172 above the beam splitter 16,instead of the indicator 17, to project the indication data such asdistance information. The indication light projected from the indicationprojector 172 is incident on the beam splitter 16 through a projectionlens 173. The light is then reflected toward the focusing plate 14 at asurface of the beam splitter 16 on which the split light is reflected,so that the light may be incident on the lower portion of the focusingplate 14. Since the projection lens 173 is adjusted to be focused on thefocusing plate 14, the lower portion of the focusing plate 14 indicates,the object distance, whether AF or MF, and whether focused or notfocused, as shown in FIG. 2. The projection of the distance informationby the indication projector 172 is controlled by the calculation/controlcircuit 23.

[0038] There is an example of operation for obtaining the objectdistance from the position of the focusing lens group 12 with referenceto FIG. 4. The lens system is an inner focus lens which forms an imageon a focusing surface P at a fixed position, by a fixed objective lensgroup L1 and a movable focusing lens group L2, likewise the case of thecollimating telescope as shown in FIG. 1. Marks G1 and G2 respectivelycorrespond to principal points of the objective lens group L1 and thefocusing lens group L2.

[0039] The following formulas may be obtained wherein: f1 is the focallength of the objective lens group L1, f2 is the focal length of thefocusing lens group L2, L is the distance from the principal point G1(of the objective lens group L1) to the focusing surface p, a is thedistance from the principal point G1 to the object 9 (hereinafter“object distance”), b is the distance from the principal point G1 to animage point I1 of the object 9 formed by the objective lens group L1, dis the distance between the principal points G1 and G2, a′ is thedistance from the principal point G2 (of the focusing lens group) to thefocal point f1 of the objective lens group L1, and b′ is the distancefrom the principal point G2 to the focusing surface p. In the followingformulas, the focal lengths f1 and f2, and the distance L from theprincipal point G1 to the focusing surface p, are invariable values solong as the image optical system is an inner focus type, and the lensdistance d+Δd is a variable number according to the object distance a.

[0040] The formula relating to imaging of the objective lens group:

1/(−a)+1/b=1/f1  (1)

[0041] The formula relating to imaging of the focusing lens group:

1/(−a′)+1/b′=1/f2  (2)

[0042] Wherein the distance L is constant, provided that b′, when a=∞ isbm′, according to the formula (2),

1/(−(f1−d))+1/bm′=1/f2

[0043] Therefore:

bm′=f2(f1−d)/(f1−d+f2)  (3)

[0044] In which, when the principal point G2 (of the focusing lens groupL2) is moved by the amount of Δd,

b′=bm′−Δd  (4)

[0045] The formula (2) may be modified as:

a′=f2×b′/(f2−b′)  (5)

[0046] Therefore, the distance d′ between the principal points G1 and G2can be obtained as follows:

d′=d+Δd  (6)

[0047] Therefore, the distance “b” to the image point I1 of the object 9is obtained by:

b=d′+a′  (7)

[0048] The formula (1) may be modified as:

a=f1×b/(f1−b)  (8)

[0049] In the above formulas, the focal lengths f1 and f2 the distancesL from the principal point G1 to the focusing surface p, and thedistance d between the lenses, are fixed. Therefore, when the movingamount of the lens Δd is measured, it is possible to obtain the objectdistance “a” by applying the formulas (3) through (8).

[0050] The above formulas relate to the operation to obtain the objectdistance for an inner focus telephotographic optical system. In the caseof telephotographic system which moves the objective lens group as awhole, the object distance “a” may be obtained by:

1/f=1/a+1/b

[0051] wherein:

a=1/(1/f−1/b).

[0052] The above formulas are the examples to obtain the object distance“a” by calculation. However, it is also possible to obtain the distanceby reading the object distance data corresponding to table data. Thetable data is recorded in a memory (EEPROM 26) by calculating therelation between the object distance “a” and the moving amount Δd of thefocusing lens group L2 in advance through calculation of everypredetermined step of the focusing lens group L2 When the moving amountof focusing lens group L2 is detected, the object distance data can beread corresponding to the table data. Tables 1 and 2 show an example ofthe corresponding relation, in which, f1=90.162 (mm), f2=−52.165 (mm),d=55.452 (mm). In this case, if the object distance “a” corresponding tothe moving amount of focusing lens group L2 which has not been processedas the table data is obtained by interpolation operation, a moreaccurate object distance “a” may be obtained. TABLE 1 Δd (Mm) b′ a′ d′ ba(mm) 0.00 103.73 34.710 55.45 90.16 −∞ 0.10 103.63 34.699 55.55 90.25−91639 0.20 103.53 34.688 55.65 90.34 −45868 0.30 103.43 34.676 55.7590.43 −30611 0.40 103.33 34.665 55.85 90.52 −22983 0.50 103.23 34.65455.95 90.61 −18406 0.60 103.13 34.643 56.05 90.69 −15354 0.70 103.0334.631 56.15 90.78 −13175 0.80 102.93 34.620 56.25 90.87 −11540 0.90102.83 34.609 56.35 90.96 −10269 1.00 102.73 34.597 56.45 91.05 −92521.10 102.63 34.586 56.55 91.14 −8420 1.20 102.53 34.575 56.65 91.23−7726 1.30 102.43 34.563 56.75 91.32 −7139 1.40 102.33 34.552 56.8591.40 −6636 1.50 102.23 34.540 56.95 91.49 −6200 1.60 102.13 34.52957.05 91.58 −5819 1.70 102.03 34.518 57.15 91.67 −5482 1.80 101.9334.506 57.25 91.76 −5183 1.90 101.83 34.495 57.35 91.85 −4916 2.00101.73 34.483 57.45 91.94 −4675 2.10 101.63 34.472 57.55 92.02 −44572.20 101.53 34.460 57.65 92.11 −4259 2.30 101.43 34.449 57.75 92.20−4078 2.40 101.33 34.437 57.85 92.29 −3912 2.50 101.23 34.426 57.9592.38 −3759 2.60 101.13 34.414 58.05 92.47 −3619 2.70 101.03 34.40258.15 92.55 −3488 2.80 100.93 34.391 58.25 92.64 −3367 2.90 100.8334.379 58.35 92.73 −3254 3.00 100.73 34.368 58.45 92.82 −3149

[0053] TABLE 2 Δd (Mm) b′ a′ d′ b a(mm) 0.094 103.64 34.699 55.55 90.25−97482 0.098 103.63 34.699 55.55 90.25 −93507 0.100 103.63 34.699 55.5590.25 −91639 0.102 103.63 34.699 55.55 90.25 −89844 0.106 103.63 34.69855.56 90.26 −86457 0.194 103.54 34.688 55.65 90.33 −47284 0.198 103.5334.688 55.65 90.34 −46331 0.200 103.53 34.688 55.65 90.34 −45868 0.202103.53 34.687 55.65 90.34 −45415 0.206 103.53 34.687 55.66 90.34 −445350.494 103.24 34.655 55.95 90.60 −18628 0.498 103.23 34.654 55.95 90.60−18479 0.500 103.23 34.654 55.95 90.61 −18406 0.502 103.23 34.654 55.9590.61 −18333 0.506 103.23 34.653 55.96 90.61 −18189 0.919 102.81 34.60656.37 90.98 −10059 0.923 102.81 34.606 56.38 90.98 −10015 0.925 102.8134.606 56.38 90.98 −9994 0.927 102.81 34.606 56.38 90.98 −9973 0.931102.80 34.605 56.38 90.99 −9930

[0054] The automatic focusing operation of the auto-level 10 isdiscussed below with reference to the flow charts shown in FIGS. 5through 11 In the present embodiment, the object distance is indicatedon the indicator 17 or by the indication projector 172 by detecting themoving amount of the focusing lens group 12 at predetermined intervalswhen the AF start switch 27 is turned ON, regardless of the automaticfocusing operation mode (AF mode) or the manual focusing operation mode(MF mode).

[0055] The following flow charts are executed by the calculation/controlcircuit 23 in a state that an unillustrated battery is loaded in theauto-level 10.

[0056] When the battery (not illustrated) is loaded, an internal RAM andinput/output ports, are firstly initialized at step S101 to subsequentlyenter the power-down operation at step S103. Thereafter, no operation atsteps S101 and S103 are performed unless the battery is unloaded and isthen reloaded.

[0057] The power-down operation corresponds to a stand-by operation inwhich the power source is OFF (except to calculation/control circuit 23and the movement detector 19) while the AF start switch 27 is OFF towait for the operation of the AF start switch 27. If the AF start switch27 is turned ON, the power source is turned ON to perform the AFoperation (automatic focusing operation).

[0058] When the power-down operation is completed, flags for the AFoperation are reset at step S105. In the illustrated embodiment, thereare several kinds of flags to be reset, including a focusing flag whichrepresents that a focused state is obtained, an AFNG flag whichrepresents that the automatic focusing operation cannot be carried out,a re-integration flag which represents that the integration operation isperformed after the focused state has been obtained, and asearch/overlap flag which is adapted to discriminate that the integraloperation is performed during movement of the focusing lens 12.

[0059] If the reset operation for the AF operation is completed, a checkis made to determine whether the AF start switch 27 is turned ON (stepS107). Since the AF start switch 27 is OFF at the initial position inwhich no operation by the operator occurs, the “OFF” data is written inthe AF start switch memory (steps S107, NO; S109). Thereafter, a checkis made to determine whether the power source is ON at step S113. Sincethe power source is OFF at the initial position in which no power issupplied to each circuit (step S113: NO), the control is returned tostep S105 and the operations at steps S107, S109 and S113 are repeated.

[0060] If the AF start switch 27 is turned ON at step S107, the controlproceeds to step S111 to check whether the AF start switch memory is ON.When the AF start switch memory is OFF (the AF start switch memory isOFF at the first time), the control proceeds to step S119 to write “ON”data in the AF start switch memory, and to start a power hold timer(steps S111, NO; S119). Thereafter, if the AF switch 29 is turned ON (inthe AF mode), the power source is turned ON to supply power to thecircuits in order to perform the VDD loop operation (steps S121; S123,YES; S125). If the AF switch 29 is OFF, which corresponds to the manualfocusing mode, the control is returned to step S101 (S123, NO; S113).

[0061] Even in the manual mode, the power source is turned ON by turningthe AF start switch 27 ON, thereby the power is supplied to each circuituntil the time of the power hold timer is up. Thus the distance isdisplayed on the indicator 17 or by the indication projector 172.

[0062] In the VDD loop operation, the automatic focusing operation iscarried out to obtain a focused state while detecting the state of theAF start switch 27, and if the focused state cannot be obtained, thecontrol is returned to step S113.

[0063] When the control enters the VDD loop operation, the state of theAF switch 29 is input again (step S210), and the control will be able toproceed provided that the AF switch 29 is ON. If the AF switch 29 isOFF, which corresponds to the manual focus mode, the control is returnedto the power-down operation (steps S201; S203, NO; S113). The followingdiscussion will be given on the assumption that the AF switch 29 is ON.

[0064] If the AF switch 29 is ON, the AF operation is performed todetect the defocus amount and accordingly move the focusing lens group12 to a focal position (steps S203, YES; S205). While the AF startswitch 27 is maintained ON, a check is made to determine whether the AFstart switch memory is ON at step S211. Since the AF start switch memoryhas been ON at step S119, the focusing flag and the AFNG flag arechecked (steps S207, YES; S211, YES; S215; S217) Since the focusing flagand the AFNG flag are both cleared if no focused state nor theimpossibility of the focusing operation are detected during the AFoperation, the control is returned to step S201 (steps S215, NO; S217,NO; S210). The operations at steps S201, S203, S205, S207, S211, S215,and S217 are repeated until either the focused state is obtained and thefocusing flag is set to “1”, or the focused state cannot be obtained andthe AFNG flag is set to “1”.

[0065] The focusing lens group 12 has been moved to the focal positionduring the AF operation at step S205, and when the focusing flag is setto “1”, the control is returned to the power-down operation (steps S215,YES; S113). If focusing cannot be effected for some reason, for example,when the aiming object moves or is too dark or is too low in contrast,the AFNG flag is set to “1” to return the control to the power-downoperation at step S101 (steps S217: YES, S113).

[0066] When the AF start switch 27 is turned OFF during the VDD loopoperation, the control proceeds from step S207 to step S209 to write“OFF” in the AF start switch memory. The control then proceeds to stepS215 by jumping step S211 (steps S207: YES, S209, S215).

[0067] Further, when the AF switch 29 is turned OFF during the VDD loopoperation, that is, when the focusing operation knob 34 is switched tothe manual focus position, the control is returned from step S203 tostep S101 to end the AF operation S203, NO; S113).

[0068] When the control is returned to the power-down operation (stepS113), a check is made to determine whether the power source is turnedON at step S113. When the power source is OFF, the control is returnedto the step S105. When the power source is ON and the power hold stateis maintained,the control is returned to step S107 (steps S113, YES;S115, YES; S107). When the power hold state is released, the control isreturned to step S105 by executing the power-down operation (steps S115,NO; S117; S105). The term “maintaining” of the power hold means that thepower hold timer has not lapsed.

[0069] The AF operation at step S205 will be described below in detailwith reference to the flow charts shown in FIGS. 7 through 9. When thecontrol enters the AF operation, the overlap flag, the search flag andthe reintegration flag are checked (steps S301, S303, S305). Since allthe flags have been cleared at step S105 at the first step, the AFsensor executes the integration and the integration result is input asAF sensor data to calculate the defocus amount (steps S301, NO; S303,NO; S305, NO; S307). As is well known, in the calculation of the defocusamount, a correlation ratio of the data of a pair of AF sensors isobtained, so that the direction of defocus (front focus or rear focus)and the defocus amount can be obtained in accordance with thecorrelation ratio.

[0070] A check is made to determine whether the calculated result iseffective at step S309. If the contrast of the aiming object is too low,or the aiming object is a repetitive pattern, or the object brightnessis too low, there is a possibility that the calculation result isineffective. An effective calculation result is usually obtained, andhence the effective calculation result will be discussed below first.

[0071] If the calculation result is effective, the focus check operationis performed. If a focused state is obtained, the focus flag is set to“1”. If a focused state is not obtained, i.e., an out-of-focus state,the focus flag is set to “0”(steps S309, YES; S321). In the illustratedembodiment, when the defocus amount is within a predetermined limit orallowance, it is considered that a focused state is obtained. If thefocused state is obtained at step S323, the control is returned to theVDD loop operation to perform the operations at step S207 and stepssubsequent thereto (step S323, YES). In the case of an out-of-focusstate, the control proceeds to the pulse calculation operation (stepS323, NO).

[0072] In the pulse calculation operation as shown in FIG. 8, the numberof AF pulses are calculated based on the effective defocus amount. Inother words, the amount of drive of the AF motor 31 (the number of AFpulses supplied from the encode 33) necessary to move the focusing lensgroup 12 until the defocus amount is zero is attained.

[0073] When the control enters the AF pulse calculation operation, thedrive direction of the AF motor 31 and the number of AF pulses arecalculated in accordance with the defocus amount (step S331). Theobtained AF pulse number is set in the AF pulse counter 23 a and the AFmotor 31 is DC-driven and the pulse checking is carried out (steps S333,S335). The value of the AF pulse counter 23 a is decreased by one everytire one AF pulse is output from the encoder 33.

[0074] In the pulse check operation, the drive speed of the AF motor 31is controlled in accordance with the value of the AF pulse counter 23 a.Namely, when the counted number is larger than theoverlap-integration-prohibition-pulse-number, the AF motor 31 is drivenat a high speed to move the focusing lens 12 toward the focal positionwithin a short space of time and the overlap integration is alsoeffected. When the counted number is smaller than theoverlap-integration-prohibition-pulse-number, although the AF motor 31is still driven at high speed, the overlap integration is prohibited. Ifthe counted number is smaller than a constant speed control start pulsenumber, the AF motor 31 is driven under PWM (Pulse Width Modulation) atlow speed to prevent the focusing lens group 12 from moving beyond thefocal position. When the counted number is zero, the AF motor 31 isstopped.

[0075] When the control enters the pulse check operation, the value ofthe AF pulse counter 23 a is compared with theoverlap-integration-prohibition-pulse-number (step S341). If the countervalue is larger than the overlap-integration-prohibition-pulse-number,the control proceeds to step S343 in which the overlap flag is set to“1”. Thereafter, the overlap integration begins, and the AF sensor datais input from the AF sensor 21 to perform the amount-of-defocuscalculation (steps S341, NO; S343; S345). If an effective calculationresult is obtained, the control proceeds to the drive direction checkoperation (step S347: YES), and if no effective calculation result isobtained, the control is returned (step S347, NO).

[0076] In the drive direction check operation as shown in FIG. 9, the AFpulse number is calculated and set in the counter, based on the AFsensor data obtained by the integration during driving of the AF motor31. If the drive direction changes, the AF motor 31 is braked andstopped. In the illustrated embodiment, the AF motor 31 is braked by theshort-circuiting of the AF motor 31 at opposite electrodes thereof.

[0077] When the control enters the drive direction check operation, theoverlap flag is set to “1”, and the search flag is set to “0” (stepS361). Thereafter, the previous and present drive directions of thefocusing lens group 12 are compared in accordance with the calculationresult (step S363). When the directions are identical with each other,the AF pulse number is calculated at an intermediate point of theintegration, so that the calculated value is set by the counter (stepsS363, YES; S365). Subsequently, the control is returned. If the drivedirection changes, the AF motor 31 is braked and stopped. Consequently,the overlap flag is set to “0” and the re-integration flag is set to“1”. Thereafter, the control is returned to the VDD loop operation(steps S363, NO; S367; S369; S371).

[0078] When the control is returned to the VDD loop operation, theoperations at step S207 and steps subsequent thereto are carried out,and the control enters the AF operation again. If no change in the drivedirection occurs, the control proceeds to the pulse check operation fromstep S301 since the overlap flag is set to “1”. The operations from stepS341 to step S347 and the operations of the drive direction checkoperation from step S361 to step S365 are carried out and the control isreturned to step S205 for the pulse check operation. These operationsare repeated until the counter value is smaller than theoverlap-integration-prohibition-pulse-number.

[0079] In the above mentioned AF operation, usually the AF pulse numbernecessary to move the focusing lens group 12 to the focal position isdecreased and becomes smaller than theoverlap-integration-prohibition-pulse-number. Thus, the control proceedsfrom step S341 to step S349 of the pulse check operation.

[0080] The operations from step S349 to step S355 stop the AF motor 31upon completion of driving of the AF motor corresponding to thecalculated AF pulse number. At step S349, control does not proceed untilthe AF pulse number is smaller than the constant speed control startpulse number. If the AF pulse number is smaller than the constant speedcontrol start pulse number, the AF motor 31 is driven at a low speed inaccordance with the remaining AF pulse number. When the AF pulse numberis zero, the AF motor 31 is stopped (steps S349, YES; S351; S353, NO).When the AF motor 31 is stopped, the overlap flag is set to “0”, and there-integrat ion flag is set to “1” (steps S353, YES; S355). Thereafter,the control is returned to the VDD loop operation.

[0081] If the control proceeds to step S205 of the VDD loop operation,the control then enters the re-integration operation at step S305, sincethe overlap flag and the search flag are set to “0” and there-integration flag is set to “1”. The same is true when the drivedirection changes at step S363.

[0082] In the re-integration operation, the defocus amount is calculatedand whether or not the telescope is focused is checked in accordancewith the defocus amount thus obtained. If a focused state is obtained,the focusing flag is set to “1”, and if a focused state is not obtained,the AF pulse is calculated again to move the focusing lens group 12.

[0083] If the control is returned to the VDD loop operation when thefocusing flag is set to “1”, the control proceeds to the power-downoperation from step S215. Thus, the AF operation ends and the controlwaits for the operation of the AF start switch 27.

[0084] The above describes the control when the focused state iscorrectly obtained. In the case that it is difficult or impossible toobtain a focused state for some reason, the control enters the VDD loopoperation and is returned to the power-down operation in an out-of-focusstate. This will be discussed below.

[0085] In the first AF operation, the integration starts, the AF sensordata is input, and the defocus amount is calculated at step S307 (stepsS301, NO; S303, NO; S305, NO; S307). If it is impossible to calculatethe effective defocus amount for some reason, for example, when theobject contrast is too low, the control proceeds to the searchintegration operation from step S309 (steps S309, NO; S311).

[0086] In the search integration operation, the integration and thedefocus calculation are carried out to obtain an effective defocusamount while driving the AF motor 31 from a close focal position to aninfinity focal position. If no effective defocus amount is obtained evenby the search integration operation, the AFNG flag is set to “1” and thecontrol is returned and enters the power-down operation at step S217.

[0087] When the control enters the search integration operation (searchoperation), the AF motor 31 is firstly search-driven (in the directionof the close focal position) and the search flag is set to “1” tocommence the integration by the AF sensor 21. When the integration iscompleted, the integral value is input as the AF sensor data tocalculate the defocus amount by defocus calculation (steps S311, S313,S315). If the effective defocus amount is obtained, the control proceedsto the drive direction checking operation (step S317, YES). If noeffective defocus amount is obtained, the control is returned to the VDDloop operation to perform the operations at step S207 and stepssubsequent thereto (steps S317, NO; S319).

[0088] The AF motor search-driving operation refers to an operation inwhich the AF motor 31 is first driven in the direction of the closefocal position and when the focusing lens 12 reaches and stops at amovement extremity on the close distance side, the AF motor 31 is drivenin the reverse direction, i.e., in the direction of the infinity focalposition. When the focusing lens group 12 reaches and stops at amovement extremity on the infinity side, the AF motor 31 is stopped. Ifan effective calculation result is obtained during the search driving,the AF motor is driven in accordance with the effective value of thedefocus amount.

[0089] When the control enters the operation at step S205 of the VDDloop operation, the overlap flag is cleared. Since the search flag isset to “1”, the control enters the search integration operation at stepS303 and the search integration operations at step S313 and stepssubsequent thereto are carried out. If no effective calculation resultis obtained when the focusing lens group 12 reaches the infinity focalposition, the control enters the AFNG operation, in which the AFNG flagis set to “1”. Thereafter, the control is returned to the VDD loopoperation and enters the power-down operation at step S217 (steps S317,NO; S319, YES; S391).

[0090] The above discussion has been directed to the case when noeffective calculation result is obtained from the beginning. Once aneffective calculation result is obtained, thereby the focusing lensgroup 12 is moved but still no focused state is obtained, if noeffective calculation result is obtained by the re-integration operation(steps S381; S383), the control proceeds to the AFNG operation from stepS385. The AFNG flag is set to “1” in the AFNG operation and thereafter,the control is returned to the VDD loop operation and enters thepower-down operation at step S217 (S385, NO; S391).

[0091] The interrupt operation, whereby the calculation/control circuit23 interrupts at regular intervals via a hard timer during executing theabove operations, will now be described with reference to FIG. 10.Firstly, the moving amount data from the reference position of thefocusing lens group 12 detected by the movement detector 19 (countervalue) are input at step S401. The amount-of-movement data isrepresented by Δd. The object distance “a” is obtained by calculationbased on the amount-of-movement data (step S403). The obtained objectdistance is displayed on the indicator 17 (step S405).

[0092] The state of the AF switch 29 is input at step S407. If the AFswitch 29 is OFF, namely the present state is not the AF mode, themanual focus mode as well as the out-of-focus state are displayed (stepsS407; S409, NO; S411; S413). Then the control is returned. If the AFswitch 29 is ON, namely the present state is the AF mode, the AF mode isdisplayed (steps S407; S409, YES; S415). Thereafter, the focusing flagis checked. If the focusing flag has been set to “1”, the focused stateis displayed (steps S417, YES; S419). Conversely, if the focusing flaghas been set to “0”, the out-of-focus state is displayed (steps S417,NO; S421).

[0093] The above interrupt operation may display the object distancecurrently focused, on the display 17 a in the visual field of theindicator 17, both in the autofocus mode and the manual focus mode.

[0094] As the operator has power of analysis and focus recognitionability via his/her eye(s), when he/she observes an object through thecollimating telescope of the auto-level 10 wherein a little defocusamount exists, he/she may feel that the image is focused even though thetelescope is not actually in the focused state. Accordingly, even ifaccurate focusing is not actually carried out, as long as the defocusamount is insignificant enough such that the operator feels the image isfocused, the focusing operation in the automatic focusing is consideredas being in a focused state. Thus the time required for focusing can bereduced, and “hunting” of the telescope can be prevented.

[0095] However, it is true that the error of the object distance willbecome larger when the object distance is obtained based on the positionof the focusing lens group 12 in which, as discussed above, a littleamount of defocus exists.

[0096] Therefore, according to a second embodiment of the presentinvention, an amount-of-defocus to be considered as being focused in theautomatic focusing operation is set within a predetermined amount, andthe object distance may be obtained with reference to theamount-of-defocus.

[0097]FIG. 11 shows the second embodiment of the present invention,which is illustrated by a flow chart of the distance indicationoperation. This distance indication is actuated according to the forcedinterruption at regular intervals by a timer, similar to the distanceindication operation shown in FIG. 10.

[0098] When the control enters this distance indication operation, thenumber of calculations is firstly cleared at step S501. The number ofcalculations relates to a counter which counts and controls the numberof calculations of the defocus amount. The lens position counter valueis then input from the movement detector 19, and the AF sensor data isalso input to calculate the defocus amount (steps S503, S505).

[0099] Thereafter, the focusing flag is checked. If the focusing flaghas been set to “1”, the number of 1 is added to the number ofcalculations, and when the present value of the number of calculationsis not N, the control is returned to step 505 (steps S507, YES; S508;S509, NO; S505) Accordingly, when the focused state is obtained, thecalculations of the defocus amount are repeated several times to improveaccuracy of calculation of the defocus amount. When the defocus amountsare calculated N times, the average of the calculated defocus amounts isobtained, and the lens position data is amended, then the controlproceeds to step S515 (steps S509, YES; S511; S513; S515). If thetelescope is in an out-of-focus state, the control jumps from step 507to step 515 (steps S507, NO; S515).

[0100] The object distance “a” is calculated at step 515 based on thelens position counter value and the lens position amended data. Thecalculated object distance “a” is then displayed in a visual field ofthe indicator 17 or by the indication projector 172 (step 517).

[0101] Thereafter, the focusing flag is checked. In the focused state,the focused state is displayed (steps S519, YES; S521), and in theout-of-focus state, the out-of-focus state is displayed (steps S519, NO;S523). Then the state of the AF switch 29 is input at step 525. In theAF mode (AF switch 29 is ON), the AF mode is displayed and the controlis returned (steps S527, YES; S529). In the manual focus mode, namelynot in the AF mode (AF switch 29 is OFF), the MF mode is displayed(steps S527, NO; S531). In the MF mode, if the defocus amount iseffective, the defocus direction and The defocus amount are displayed,and the control is returned (steps S533, YES; S535). If the defocusamount is not effective, the control is returned by jumping step 535(step 533, NO).

[0102] According to the second embodiment of the present invention, theobject distance is displayed by not only using the position of thefocusing lens group 12, but also using the defocus amount detected bythe AF sensor 21, thus an accurate object distance may be detected anddisplayed.

[0103] In addition, according to an aspect of the present embodiment,the defocus direction and the defocus amount are displayed, it ispossible to confirm whether the accurate focused state is obtained, andin the case of an out-of-focus state, it is possible to confirm whetherthe present state is front focus or rear focus, as well as the amount oferror thereof.

[0104] Although the distance information is displayed in the visualfield according to the above embodiments as above illustrated, thedisplay is not limited to be positioned in the visual field, and may bepositioned outside the optical instrument. In addition, although theabove embodiments are applied to an auto-level, the present inventioncan be equally applied to other surveying instruments, such as a transitor a total station, as well as a telescopic optical system such as atelescope or a binocular telescope, etc.

[0105] As may be understood from the foregoing, according to the presentinvention, the object distance is indicated in the visual field ofobservation, by obtaining the object distance from the position of thefocusing lens group, in regard to the optical instrument in which thefocusing is carried out by moving the focusing lens group. Thus theoperator can easily confirm the object distance during observing theobject.

[0106] Further, according to the present invention as claimed in claim13 below, there is a device to detect the defocus amount, and theposition of the focusing lens group is amended according to the defocusamount detected by the defocus amount detecting device. Thus an accurateobject distance can be detected.

What is claimed is:
 1. An indicator for an optical instrument includingan observational optical system to observe an image formed by anobjective optical system having a focusing lens group, comprising: alens position detecting device to detect a position of said focusinglens group; a distance detecting device to obtain an object distanceaccording to a position of said focusing lens group detected by saidlens position detecting device; and a display device to display anobject distance detected by said distance detecting device.
 2. Anindicator for an optical instrument according to claim 1 , wherein saiddisplay device is an inside-visual-field display device which displaysinformation of said object distance in a visual field of saidobservational optical system.
 3. An indicator for an optical instrumentaccording to claim 1 , wherein said optical instrument is a telescopecomprising, in order from the object side, a fixed objective lens group,a movable focusing lens group, an erecting optical system and aneyepiece lens group.
 4. An indicator for an optical instrument accordingto claim 1 , wherein said optical instrument is a collimating telescopeof an auto-level comprising, in order from the object side, a fixedobjective lens group, a movable focusing lens group, a horizontalcompensation optical system, a focusing plate and an eyepiece lensgroup.
 5. An indicator for an optical instrument according to claim 4 ,wherein a display of said display device is provided in the periphery ofsaid focusing plate.
 6. An indicator for an optical instrument accordingto claim 5 , wherein said optical instrument further comprises: a splitoptical system between said horizontal compensation optical system andsaid focusing plate; an AF sensor unit to detect a focusing state byreceiving light divided by reflection in said split optical system; anda lens driving device to move said focusing lens group according to afocusing state detected by said AF sensor unit.
 7. An indicator for anoptical instrument according to claim 6 , wherein saidinside-visual-field display device further comprises a projectionoptical system, which emits information of said object distance on saidspilt optical system, to project said information of said objectdistance on the periphery of said focusing plate through reflection bysaid split optical system.
 8. An indicator for an optical instrumentaccording to claim 6 , wherein said optical instrument further comprisesa manual focusing operation device which manually moves said focusinglens group.
 9. An indicator for an optical instrument according to claim8 , wherein said distance detecting device displays by said displaydevice through detecting said object distance when any operation to movesaid focusing lens group is executed.
 10. An indicator for an opticalinstrument according to claim 1 , wherein said distance detecting devicecalculates said object distance according to a moving amount from areference position of said focusing lens group detected by said lensposition detecting device.
 11. An indicator for an optical instrumentaccording to claim 1 further comprising a memory, wherein said distancedetecting device selects said object distance from table datacorresponding to a position of said focusing lens group detected by saidlens position detecting device.
 12. An indicator for an opticalinstrument according to claim 6 , further comprising an AF start switch,wherein said distance detecting device is actuated, after said lensdriving device is stopped by operation of said AF start switch, todisplay a detected object distance on said display device for apredetermined time.
 13. An indicator for an optical instrument includingan observational optical system to observe an image formed on apredetermined focal plane by an objective optical system having afocusing lens group, comprising: a split optical system positionedbetween said objective optical system and said observational opticalsystem; a focusing detecting device to detect a defocus amount at aposition equivalent to said focal plane by receiving light divided bysaid split optical system; a lens driving device to drive said focusinglens group according to a defocus amount detected by said focusingdetecting device so that said defocus amount becomes a smallest value; alens position detecting device to detect a position of said focusinglens group; an object distance detecting device to obtain an objectdistance according to a position of said focusing lens group detected bysaid lens position detecting device and according to said defocusamount; and a display device to display an object distance detected bysaid object distance detecting device.
 14. An indicator for an opticalinstrument according to claim 13 , wherein said display device is aninside-visual-field display device which displays information of saidobject distance in a visual field of said observational optical system.15. An indicator for an optical instrument according to claim 13 ,wherein said lens driving device stops movement of said focusing lensgroup when an absolute value of defocus amount detected by said focusingdetecting device becomes smaller than a predetermined value.
 16. Anindicator for an optical instrument according to claim 15 , wherein saidobject distance detecting device lo obtains an object distance as anaverage of plural times of calculation of defocus amount via saidfocusing detecting device, after said lens driving device stops movementof said focusing lens group.
 17. An indicator for an optical instrumentaccording to claim 13 , wherein said display device displays, other thansaid object distance information, at least one from among the followinginformation: focused/out-of-focus, the defocus direction, or theamount-of-defocus.
 18. An indicator for an optical instrument accordingto claim 13 , wherein said optical instrument is a telescope comprising,in an order from the object side, a fixed objective lens group, amovable focusing lens group, an erecting optical system and an eyepiecelens group.
 19. An indicator for an optical instrument according toclaim 13 , wherein said optical instrument is a collimating telescope ofan auto-level comprising, in an order from the object side, a fixedobjective lens group, a movable focusing lens group, a horizontalcompensation and erecting optical system, a split optical system, afocusing plate and an eyepiece lens group.
 20. An indicator for anoptical instrument according to claim 19 , wherein saidinside-visual-field display device further comprises a display in theperiphery of said focusing plate.
 21. An indicator for an opticalinstrument according to claim 19 , wherein said inside-visual-fielddisplay device further comprises a projection optical system, whichemits information of said object distance on said spilt optical system,to project said information of said object distance on the periphery ofsaid focusing plate through reflection by said split optical system. 22.An indicator for an optical instrument according to claim 13 , whereinsaid optical instrument further comprises a manual focusing operationdevice which allows said focusing lens group to be manually adjusted.23. An indicator for an optical instrument according to claim 13 ,wherein said distance detecting device displays said object distance viasaid display device by detecting said object distance when any operationto move said focusing lens group is executed.
 24. An indicator for anoptical instrument according to claim 13 , wherein said distancedetecting device calculates said object distance according to a movingamount from a reference position of said focusing lens group detected bysaid lens position detecting device and according to said defocusamount.
 25. An indicator for an optical instrument according to claim 13, further comprising an AF start switch, wherein said distance detectingdevice is actuated, after said lens lo driving device is stopped via theoperation of said AF start switch, to display a detected object distanceon said display device for a predetermined time.
 26. An opticalapparatus for a surveying instrument comprising: a telescopic opticalsystem comprising: an objective lens group; a focusing lens group; afocusing plate; an eyepiece lens group for viewing images of objectsformed on said focusing plate via said objective lens group and saidfocusing lens group; a lens position detecting device which detects theamount of movement of said focusing lens group from a predeterminedreference position; an object distance detecting device which detectsthe object distance with respect to the position of said focusing lensgroup according to the detected said amount of movement via said lensposition detecting device; a display device for displaying the detectedobject distance according to said object distance detecting device. 27.An optical apparatus for a surveying instrument according to claim 26 ,wherein said object distance detecting device calculates the objectdistance based on: the amount of movement of said focusing lens groupobtained from said lens position detecting device, the previouslydetermined focal length of said objective lens group, the focal lengthof said focusing lens group, and the distance between said objectivelens group and the focusing lens group at the reference position.
 28. Anoptical apparatus for a surveying instrument according to claim 26 ,wherein said optical apparatus further comprises a memory for storingtable data on the relationship between the amount of movement of saidfocusing lens group from said reference position and the objectdistance; said object distance detecting device detects said objectdistance by selecting from said memory the object distance correspondingto said amount of movement based on the amount of movement of saidfocusing lens group detected by said lens position detecting device. 29.An optical apparatus for a surveying instrument according to claim 26 ,wherein said optical apparatus further comprises: a beam splittingoptical system located between said focusing lens group and saidfocusing plate; a focus detecting device, which receives a spit beamwhich has been split by said beam splitting optical system, fordetecting the amount of defocus of an object at a position equivalent tothe position of said focusing plate; said object distance detectingdevice detects the corrected object distance by incorporating an averageof a plurality of defocus amounts obtained by said focus detectingdevice.
 30. An optical apparatus for a surveying instrument according toclaim 26 , wherein said optical apparatus further comprises: a beamsplitting optical system located between said focusing lens group andsaid focusing plate; a focus detecting device, which receives a spitbeam which has been split by said beam splitting optical system, fordetecting the defocus direction and amount of defocus of an object at aposition equivalent to the position of the focusing plate; said displaydevice displays, in addition to the object distance, at least one of thefollowing: focused/out-of-focus, the defocus direction, or theamount-of-defocus.